The present invention relates to ethylene oxide sterilization process indicators and, more particularly, to chemical indicator inks that are designed to undergo an irreversible color change when exposed to ethylene oxide vapor in the presence of low-temperature steam, and to methods for indicating that an article has undergone ethylene oxide sterilization processing.
Biological and medical operations such as hospitals, medical laboratories and other allied health facilities, which often come in contact with microorganisms and other microbiological agents, employ a variety of technology to control both infection and contamination. While compositions such as germicides, antiseptics and bacteriostats are effective in controlling widespread growth of biological contaminants, they do not go as far as to completely eliminate these agents.
Since many of the materials and instruments that are used in modern hospitals must be kept sterile, but cannot withstand the heat and/or moisture encountered in a conventional steam sterilization process, there is a growing trend towards the use of an alkylating agent as the sterilization agent. The most popular sterilization alkylating agent presently employed is ethylene oxide gas, generally in an admixture with an inert gaseous diluant such as carbon dioxide, nitrogen, tricloromonofluoromethane, dichlorodifluoromethane, and the like. Ethylene oxide gas can be used as a sporicidal and virucidal agent. Consequently, ethylene oxide sterilization processes are often employed to ensure total eradication of microorganisms.
Since ethylene oxide gas readily diffuses through all of the commonly employed packaging materials and is highly effective in killing microorganisms at temperatures well below those required for heat sterilization techniques, it enables efficient sterilization of many items, particularly those made of thermoplastic materials, which cannot withstand heat sterilization. The process generally involves placing an item in a chamber and subjecting it to ethylene oxide vapor. When used properly, ethylene oxide is not only lethal to all known microorganisms at ordinary temperature, but it is also non-corrosive, readily removed by aeration, easily handled and stored, and has a low toxicity to humans.
Known in the art are methods for indicating that an article has undergone ethylene oxide sterilization. For example, U.S. Pat. Nos. 2,998,306 and 3,098,751 teach methods employing water-based and solvent-based chemical indicators, respectively, which undergo an irreversible color change when placed in an ethylene oxide environment. However, the number of color changes available from these indicators is limited. Moreover, the organic solvents employed in some of these chemical indicators present an environmental hazard. Thus, there is a need for chemical indicator inks that exhibit additional color changes upon exposure to ethylene oxide vapor in the presence of low-temperature steam and do not contain high concentrations of volatile organic compounds.
The present invention meets this need by providing water-based chemical indicator inks that contain at least one pH indicator dye. The inks are effective in showing whether or not treated materials have been subjected to sterilizing conditions using ethylene oxide as the sterilization medium.
In accordance with one aspect of the present invention, a water-based chemical indicator ink for ethylene oxide sterilization processes is provided containing at least one pH indicator dye selected from the group consisting of Bromocresol green, Bromophenol blue, Methyl red, Ethyl orange, and combinations thereof. The pH indicator dye undergoes an irreversible color change when exposed to ethylene oxide vapor in the presence of low-temperature steam. The low-temperature steam has a temperature of less than about 145xc2x0 F. Moreover, the pH indicator dye when exposed to other sterilization processes such as formaldehyde gas, high-temperature steam, dry heat, or combinations thereof, either does not undergo a color change or undergoes a color change that is different than is obtained when exposed to ethylene oxide vapor.
The water-based chemical indicator ink can comprise a solution including the pH indicator dye dissolved in water. The water-based chemical indicator ink can further contain a powdered and crystallized hexahydrate metal salt. In addition, the water-based chemical indicator ink can further contain an acidic compound such as citric acid, at least one thickening agent, a white pigment such as titanium dioxide, a binder, and/or a foam suppressor such as an aliphatic polyol blend. The acidic compound retards a color change of the water-based chemical indicator ink. The thickening agent can be selected from the group consisting of hydrous aluminum silicates, hydrous magnesium silicates, and combinations thereof. The binder can be a polymeric material selected from the group consisting of polyvinyl alcohol, methyl cellulose, and combinations thereof.
In accordance with another aspect of the present invention, a method is provided for indicating that an article has undergone ethylene oxide sterilization processing. The method comprises providing a water-based chemical indicator ink containing at least one pH indicator dye selected from the group consisting of Bromocresol green, Bromophenol blue, Methyl red, Ethyl orange, and combinations thereof. The pH indicator dye undergoes an irreversible color change when exposed to ethylene oxide vapor in the presence of low-temperature steam. The method further comprises applying the water-based chemical indicator ink to an article, subjecting the article to a concentration of ethylene oxide vapor in the presence of low-temperature steam, and observing the chemical indicator ink for a color change that is visually indicative of whether the concentration of ethylene oxide vapor has been applied for a time sufficient to sterilize the article.
The method can further comprise measuring the integrated effect of subjecting the article to the concentration of ethylene oxide vapor in the presence of low-temperature steam for the time sufficient to sterilize the article. In addition, the method can comprise applying the water-based chemical indicator ink to a substrate to form an ethylene oxide sterilization process indicator prior to applying the ink to the article. The step of applying the water-based chemical indicator ink to a substrate can be accomplished by printing the ink on the substrate in the shape of squares or insignia to form the indicator. In addition, the indicator can be secured to a package containing the article and subjected to the concentration of ethylene oxide vapor in the presence of low-temperature steam.
Accordingly, it is a feature of the present invention to provide a water-based chemical indicator ink for printing insignia on a substrate that is visually indicative of whether a concentration of ethylene oxide has been applied for a time sufficient to ensure sterilization within a treating chamber or within the contents of a package subjected to ethylene oxide gas treatment therein. It is also a feature of the present invention to provide a printed informative device for ethylene oxide sterilization, which is cost effective, relatively simple to use, resists contaminating the goods being sterilized, and is environmentally friendly. This and other features and advantages of the present invention will become apparent from the following detailed description and the appended claims.